1. Field of the Invention
The present invention relates to optical components having refractive index gradients, to their use, to methods of producing them via organic-inorganic hybrid materials, and to said hybrid materials.
2. Discussion of Background Information
It is known that the diffusion of monomers whose refractive index is higher or else lower than that of the surrounding liquid matrix can be utilized for the production of a refractive index gradient, as described for example in U.S. Pat. No. 5,552,261 and U.S. Pat. No. 5,529,473. The Colburn-Haines effect known for photopolymers and relating to directed diffusion with subsequent polymerization in the heated or exposed areas, leads to an increase in density and hence to an increase or reduction in the refractive index (RI). In the case of organic monomers, however, this change is small, since the change in density which comes about makes only a small contribution to the molar refraction. The RI gradient profile is fixed thereafter by aftercrosslinking, by way of photopolymerization for example.
Disadvantages of these materials are relatively small RI increases, long operating times, and high scattering losses. From WO 97/38333 it is known that RI gradients can also be produced by way of the migration of nanoparticles of high or low refractive index in a liquid, photopolymerizable matrix (sol) and fixed by way of subsequent crosslinking (polymerization, condensation). The key drawback of that process is that it is tied to a liquid matrix phase. Consequently, handling problems arise with the application of holographic techniques or mask exposure techniques.
A further factor is that the RI differences in polymers, even via the Colburn-Haines effect, are relatively small, owing to the physical properties of the material. Other studies describe the diffusion of nanoparticles in incompletely compacted polymer matrices under the influence of gradient-forming measures, such as, for example, A. Zimmermann et al., Light-Management Films Based on Nanocomposite Coatings, paper at 5th Int. Conf. Coatings on Glass, Saarbrücken, Germany, 4 to 8 Jul. 2004. The RI difference is achieved by concentrating relatively high-RI inorganic nanoparticles. A drawback of that process is that the diffusion rate of the particles is smaller by one or more orders of magnitude than that of organic monomers, and the operation necessarily entails the presence of hydrolysable or hydrolysed silanes. These silanes give the materials a relatively high moisture sensitivity (e.g. C. J. Brinker, G. W. Scherer, Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing, Academic Press 1990).
DE-A-10200648 describes a process for producing holographic films and diffuser films, in which nanoparticles in conjunction with hydrolysable or hydrolysed silanes are vital to the production of holographic structures. These compounds and their preparation each exhibit the drawbacks referred to above. Condensation of the silanes may also lead to three-dimensional crosslinking and hence to the embrittlement of the material.
It is an object of the present invention, therefore, to develop a material capable of building up a sufficiently high RI gradient by application of external fields or use of gradient-forming measures, which does not have the aforementioned drawbacks, in particular the drawbacks due to the silanes, such as, for example, the high moisture sensitivity, caused by the high proportion of uncrosslinked residual OH groups, and the inorganic three-dimensional crosslinking caused by condensation of the silanes, and hence embrittlement of the material.
It has now surprisingly been found that this object can be accomplished by means of a polymer which forms a solid or viscous matrix and in which certain metal complex compounds are dispersed or dissolved, without the need for silanes.